This invention relates to an apparatus for transferring a pattern of an original or an apparatus for forming an image with the use of an electron beam or a laser beam.
Projection type image forming apparatus such as an exposure apparatus for transferring, onto a radiation-sensitive or photosensitive wafer, a fine pattern formed on a mask or reticle (which will hereinafter be also referred to simply as a "mask") through a proximity process or with a projection optical system; an exposure apparatus for forming a fine pattern on a wafer through the scan of an electron beam; or a laser beam printer for forming a fine image on a photosensitive or radiation-sensitive member through the scan of a laser beam are distinguished from contact type image forming apparatus such as a semiconductor exposure apparatus of contact type in that, in the former types, the image is projected onto the radiation-sensitive or photosensitive member via a "space", which leads to a problem of positional deviation or displacement between the image to be projected and the sensitive member due to the vibration caused within the apparatus itself or generated by any external cause.
The projection type image forming apparatus as mentioned above has not employed any means for detecting the image fluctuation due to the vibration. Rather, a vibroisolating stage has been employed to absorb the vibration transmitted from the floor to suppress transfer of the vibration to the apparatus. In addition, with respect to the vibration which might be caused within the apparatus itself, the inertial mass or moving speed of each of various movable parts of the apparatus has been decreased to minimize the occurrence of the vibration.
Further, in view of the fact that the vibration caused by the movement of the movable parts is damped or attenuated after the lapse of a predetermined time period past the completion of the movement so that the relative amplitude is decreased, a suitable delay time has been selected on the basis of experimental results on the damping time, and the apparatus has been arranged so that, after the lapse of this delay time past the completion of the movement of the movable parts, the succeeding step such as exposure is initiated. Since, however, the moving speed should generally be high where the amount of movement of the movable part is large, the damping time in such case is accordingly longer. Therefore, a longer delay time is usually selected for the purpose of ensuring reliable operation. The selection of such longer delay time which is fixed is, however, not so advantageous in a case where the amount of movement is small, since the waste of time leads to a decreased throughput.
Moreover, if a vibration which is not sufficiently attenuated within the preset delay time occurs due to any external cause such as an earthquake, the succeeding exposure step or the like would be carried out without correcting the positional deviation or displacement between the image to be projected and the sensitive member.